Artaud et al., C. R. Hebd. Seances Acad. Sci., Ser. C. (1976) 283 (11) 503-5 (C.A. 87:5424 (1977)) report on the study of cyclopropane formation from alpha-chloro esters. The cycloaddition reaction is carried out in aprotic media; tetrabutylammonium bromide is added as a catalyst.
Starks, "Selecting a Phase Transfer Catalyst", Chemtech 1980 (2), 110-117 discusses the use of quaternary ammonium and phosphonium salts as phase transfer catalysts. Preferred ammonium and phosphonium salts are those having at least one large alkyl group (e.g. C.sub.16 H.sub.33). In general, large cations are better catalysts than small cations (e.g., the tetrabutylammonium cation is a better catalyst than the tetrapropylammonium cation or the tetramethylammonium cation).